Portable radio communication apparatus

Abstract: In a portable radio communication apparatus, a matching circuit is electrically connected to an antenna when the antenna is retracted into a casing. In this condition, the antenna and a feed circuit are matched as desirably as when the antenna is extended from the casing.

Description: BACKGROUND OF THE INVENTION The present invention relates to an improvement in a cordless telephone, transceiver or similar portable radio communication apparatus. Particularly, the present invention relates to a portable radio communication apparatus according to the preamble part of claim 1 and to a rod antenna according to the preamble part of claim 4. Such a portable radio communication apparatus and such a rod antenna are known from US-A-4 890 114. Today, a portable radio communication apparatus of the kind described is often put in the user's bag or even in a pocket by virtue of remarkable miniaturization. Usually, this kind of apparatus has a casing and an antenna retractably mounted on the casing. The antenna is retracted into the casing when the apparatus is simply carried by the user or extend from the casing when the apparatus is to be used. Hence, when the apparatus is waiting for an incoming call, the antenna is, in many cases, received in the casing. This brings about a problem that the antenna in the retracted position cannot attain a sufficient characteristic, reducing the transmission/reception range to a critical degree. What is important is, therefore, to enhance the antenna characteristic when the antenna is held in the retracted position. On the other hand, it has been customary with the apparatus of the kind described to match the antenna and a feed circuit by a matching section, which is included in the feed circuit, such that an optimal condition is set up when the antenna is extended from the casing. It follows that in the retracted position, the antenna and the feed circuit cannot be matched, noticeably degrading the antenna characteristic. As a result, the apparatus is prevented from performing communication stably. In GB-A-2 235 588 a telescopic antenna is disclosed. The lower end of the telescopic antenna in the collapsed position is in contact with a matching circuit. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a portable radio communication apparatus capable of matching, when an antenna is retracted into a casing, an antenna and a feed circuit as desirably as when the antenna is extended from the casing, thereby enhancing the antenna characteristic. This object is achieved by a portable radio communication apparatus as defined in claim 1 and a rod antenna as defined in claim 4. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: FIG. 1A shows a first example of a radio communication apparatus which example is usefull for the understanding of the invention in a condition wherein an antenna is retracted into a casing; FIG. 1B shows the first example in a condition wherein the antenna is extended from the casing; FIG. 2A shows a second example of a radio communication apparatus which example is usefull for the understanding of the invention in a condition wherein an antenna is retracted into a casing; FIG. 2B shows the second example in a condition wherein the antenna is extended from the casing; FIGS. 3A and 3B each shows a specific configuration of a matching circuit included in the embodiments; FIGS. 4A and 4B each shows specific means for connecting the antenna and matching circuit included in the examples; and Fig. 5 shows a specific configuration of the antenna included in the embodiment of the invention and specific means for connecting the antenna and a feed circuit at a feed point. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1A and 1B of the drawings, a first example of a portable radio communication apparatus which example is usefull for the understanding of the invention is shown and includes a casing 11. A transmission/reception circuit 12, a feed circuit 13, and a matching circuit 14 are accommodated in the casing 11. An antenna element, or simply antenna, 15 is mounted on and retractable into the casing 11. As shown in FIG. 1A, when the antenna 15 is retracted into the casing 11, it is electrically connected to the feed circuit 13 at a feed point 16 and, therefore, connected to the transmission/reception circuit 12 via the feed circuit 13. The lower end of the antenna 15 is electrically connected to the matching circuit 14. In this condition, the matching circuit 14 opens the impedance from the feed circuit 13 to the direction of the antenna 15 indicated by an arrow B with respect to the frequency assigned to the radio apparatus. Also, a matching section, not shown, included in the feed circuit 13 adjusts the impedance from the feed circuit 13 to the direction of the antenna 15 indicated by an arrow A to an adequate characteristic impedance, e.g., 50 Ω. With this configuration, the radio apparatus is free from the influence of the antenna 15 in the direction B and, therefore, operable in a stable manner even when the antenna 15 is retracted into the casing 11. As shown in FIG. 1B, when the antenna 15 is extended from the casing 11, it is not electrically connected to the matching circuit 14 although it is electrically connected to the feed circuit 13 at the feed point 16. In this condition, the matching section of the feed circuit 13 adjusts the impedance from the feed circuit 13 to the antenna 15 to an adequate characteristic impedance, e.g., 50 Ω. A reference will be made to FIGS. 2A and 2B for describing a second example being usefull for the understanding of the invention. In FIGS. 2A and 2B, the same or similar constituent parts as or to the parts of FIGS. 1A and 1B are designated by the same reference numerals, and a detailed description thereof will not be made in order to avoid redundancy. As shown, this example is similar to the previous example except that a conductor in the form of a coil 31 is connected to the antenna 15. The matching circuit 14 opens the impedance from the feed circuit 13 to the direction B of the antenna 15 with respect to the assigned frequency, as in the first embodiment. Regarding the impedance from the feed circuit 13 to the direction A of the antenna 15, the matching section of the feed section 13 adjusts it to an adequate characteristic impedance, e.g., 50 Ω. FIGS. 3A and 3B each shows a specific configuration of the matching circuit 14 included in the embodiments of the invention. As shown, the matching circuit 14 may be implemented by a capacitor 14a, as shown in FIG. 3A, or by an inductor 14b, as shown in FIG. 3B. FIGS. 4A and 4B each shows specific means for connecting the matching circuit 14 and antenna 15 also included in the embodiments. FIG. 4A shows connecting means 20 provided on the matching circuit 14. The connecting means 20 is so configured as to nip the lower end of the antenna 15 when the antenna 15 is retracted into the casing 11. FIG. 4B shows connecting means 21 which is provided on the lower end of the antenna 15. Referring to Fig. 5 there will be described specific configurations of the antenna 15 and specific means for connecting the antenna 15 and feed circuit 13 at the feed point 16. Fig. 5 shows an antenna 15B whose surface is entirely covered with an insulator. In this case, therefore, connecting means 28 is implemented as a metallic member which does not contact the antenna 15B. In summary, it will be seen that the present invention provides a portable radio communication apparatus which enhances, when an antenna thereof is held in a retracted position, the antenna gain and performs communication stably. This unprecedented advantage is derived from a unique matching circuit which is electrically connected to the antenna when the antenna is retracted into a casing. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Claims: A portable radio communication apparatus comprising: a transmission/reception circuit (12); a casing (11) accomodating said transmission/reception circuit (12); an antenna rod (15) mounted on and retractable into said casing; and sliding relative to a feed point (16); a feed circuit (13) accomodated in said casing (11) for electrically connecting said antenna (15) and said transmission/reception circuit (13) at said feed point (16); and a matching circuit (14) accomodated in said casing; characterized in that said matching circuit (14) is coupled to the bottom tip of said antenna rod (15), when said antenna rod is retracted into said casing (11), said matching circuit (14) opening impedance of said antenna rod (15) from said feed point (16) to said bottom tip such that the radio communication apparatus is free from influence of the antenna rod (15) between said feedpoint (16) and said bottom tip, wherein said antenna rod (15) comprises a conductive rod having its entire surface covered with an insulator and in that a first connecting means is provided comprising a metallic loop member (28) co-axially around the antenna rod which does not contact said antenna rod for connecting said feed circuit and said antenna rod. An apparatus as claimed in claim 1, further comprising a conductor connected to said antenna rod (15) and implemented as a coil (31). An apparatus as claimed in claim 1, further comprising second connecting means (20, 21) for coupling said antenna rod and said matching circuit (14) when said antenna is retracted into said casing. A rod antenna having a matched impedance in both an extended position and in a retracted position, comprising: an antenna rod (15) slidably mounted in a casing (11), said antenna rod having an outer surface portion, a lower end, and an upper end; a feed circuit (13) positioned at said casing for providing an electrical feed to said antenna rod; said antenna rod being slidable relative to said feed circuit; characterized by a matching circuit (14) positioned to electrically couple said lower end of said antenna rod (15) when said antenna rod (15) is in said retracted position and for putting a matching impedance in series between the lower end of said antenna rod and electrical ground, wherein said antenna rod is covered with an electric insulator and said feed circuit comprises a conductive loop (28) co-axial around said antenna rod. A rod antenna as recited in claim 4, wherein said feed circuit (13) matches impedance of said antenna rod (15) from said feed circuit to said upper end in both the retracted position and in the extended position of said antenna rod. A rod antenna as recited in claim 4, wherein the upper end of said antenna rod comprises a coil (31). A rod antenna as recited in claim 4, wherein said matching circuit comprises a capacitor (14a) connecting said lower end of said antenna rod to said electrical ground. A rod antenna as recited in claim 4, wherein said matching circuit (14) comprises an inductor (14b) connecting said lower end of said antenna rod to said electrical ground.

Inventors: IMURA MINORU, IMURA, MINORU, IMURA, MINORU, C/O NEC COPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: H04B1
IPC codes: H04B1, H04Q7, H01Q1